The present invention relates to a light source unit and projection display system for combining certain wavelengths of light from LED light sources or laser light sources and projecting the combined wavelengths of light onto a screen by the use of an image display device.
In recent years, single-color LED light sources of red, green, and blue colors producing higher output and semiconductor lasers of red, green, and blue colors producing higher output have been fabricated. Consequently, small-sized projectors using these light sources have enjoyed wider acceptance in the market.
Known image display devices used in small-sized projectors include LCOS (liquid crystal on silicon) being reflective liquid crystal displays, DMD (digital micromirror device), and MEMS (Microelectromechanical Systems) mirrors scanned in two dimensions.
In these small-sized projectors, output wavelengths of light from monochrome LEDs of three colors or from semiconductor lasers are combined into one and visualized by an image display device such as LCOS or DMD. In MEMS mirror technology, the output colors of light from monochrome LEDs of three colors or semiconductor lasers are combined in one optical path, and light is scanned for each color in turn to display a visible image.
U.S. Pat. No. 8,238,029 (patent literature 1) discloses a technique for combining beams of light emitted from monochrome LEDs of three colors or from semiconductor lasers by a dichroic mirror consisting of surfaces which are different in wavelength selectivity.
Where colors of light from monochrome light sources of three colors are shone on a single image display device, it is necessary to provide a means for combining light sources of red, green, and blue into one common optical system. Where separate optical elements are used to combine three colors, the number of components is increased and the whole light source unit is increased in size. This is disadvantageous for miniaturization and cost reduction.
According to the technique disclosed in patent literature 1, three colors of light can be combined using one dichroic mirror but combination of beams of light projected onto an MEMS mirror is described. However, use of image display devices using two-dimensional light sources such as LCOS or DMD is not taken into account.